Three Afghan-Canadian immigrants accused of drowning four relatives in a so-called "honour killing" should be set free, and the people responsible for the investigation arrested and charged, the defendants' murder trial was told Tuesday.

The suggestion came from defence witness Dr. Mohammad Anwar Yaqubi, the younger half-brother of businessman Mohammad Shafia. A physician who now lives in the Netherlands, Dr. Yaqubi was the second-last witness to be called in the trial, now in its third month.

At issue were remarks overheard on police wiretaps and entered as evidence in which Mr. Shafia cursed his three dead daughters as "whores," "filthy," and "shameless," and used many other epithets.

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His brother has been misunderstood, Dr. Yaqubi told the court.

Together with his second wife and eldest son, Mr. Shafia is charged with four counts of first-degree murder – "honour killings," the Crown says, committed primarily to cleanse the family of disgrace.

The prosecution alleges the four deaths at the Kingston Mills locks, just east of Kingston, Ont., were preceded by years of violence and abuse by the three defendants.

Dr. Yaqubi, however, told the trial that although his contact with the Shafia family had for many years been very limited, he spoke several times with Mr. Shafia's first wife, Rona Amir Mohammad, one of the four people the defendants are accused of killing, and that she never mentioned any domestic troubles.

And as for the language Mr. Shafia used about the dead women, which included the remark, "May the Devil shit on their graves," it resulted from grief and stress, Dr. Yaqubi said, telling the court he had listened to all the wiretapped conversations, recorded in the run-up to the arrests.

"Those are statements that would exonerate my brother," he said. "If you analyze them properly you will see that dear Shafi (Mr. Shafia) should not be here. I think they should be released and the people in charge of the investigation should be charged."

The wiretaps had been selectively "censored," he claimed, because "I know this is not the place for my brother to be because he is not a murderer. There is no sin greater than murder – or to accuse somebody of it."

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He also echoed his sister, who testified Tuesday, in stating that he had never heard of the concept of honour killings, either in Afghanistan or in the Netherlands.

Prosecutor Gerard Laarhuis then asked him if it would be offensive in Afghanistan for fathers to use such language about their daughters, just days after they died.

That would depend, he replied, because his homeland is a complex place. "Different families do different things."

On June 30, 2009, the drowned bodies of Zainab, Sahar and Geeti Shafia, aged 19, 17 and 13, were found in a Nissan Sentra submerged at Kingston Mills Locks, which connects the Rideau Canal to the Cataraqui River and Lake Ontario.

Also in the vehicle was Ms. Mohammad, 53, Mr. Shafia's first wife, who helped raise the seven children in a clandestine polygamous marriage. The family had immigrated to Canada two years earlier.

The defendants insist a bizarre accident occurred, but from the outset detectives suspected murder.

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The accused say the Nissan ended up under water after Zainab and the other three borrowed it for a late-night spin, as the family stayed at a Kingston motel en route home to Montreal from a brief holiday in Niagara Falls.

The prosecution, however, is certain that under cover of darkness the Nissan was pushed into the lock by the second car, a Lexus SUV, in which the 10-member family was travelling.

Dr. Yaqubi also emphasized his view that Ms. Mohammad, Mr. Shafia's dead first wife, seemed to be an equal partner within the polygamous marriage, although he agreed her sister in France, with whom she stayed before relocating in Quebec, had urged her to get a divorce and a financial settlement.

Central to the prosecution's case is the thesis that Ms. Mohammad was in no way an equal, but rather was routinely mistreated, ostracized and treated as a servant. Her uncertain status as Mr. Shafia's first wife, moreover, (her husband told immigration authorities she was a cousin) posed a threat to the family's residency in Canada.

But as with much else that forms the basis of the prosecution case – police visits to the family's Montreal home, unhappy behaviour by the children that included a suicide attempt, repeated absenteeism from school – Dr. Yaqubi agreed he had little first-hand information.

"You really had no idea about the problems going on in your brother's family did you?" Mr. Laarhuis asked him.

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